The present invention relates generally to a device and method for treating a blockage or stenosis in a vessel of a patient. More specifically, the present invention relates to a device and method for precisely delivering a dosage of radiation to a vessel to inhibit re-stenosis.
It is well known that many medical complications are caused by a partial or total blockage or stenosis of a blood vessel in a patient. Depending on the location of the stenosis, the patient can experience cardiac arrest, stroke or necrosis of tissues or organs. Commonly, the stenosis is caused by the build-up of artherosclerotic plaque in the intima of the vessel. The plaque typically builds up irregularly in the vessel. As a result of the irregular build-up of plaque, the lumen of the vessel, in most blocked vessels, is not centrally located relative to the external elastic lamina.
Several procedures have been developed to treat stenoses, including angioplasty, stenting, and atherectomy. However, none of these procedures are entirely successful in inhibiting or preventing the re-stenosis of a vessel after the procedure is completed.
Recent studies have demonstrated that radiation may inhibit or prevent re-stenosis in the vessel by inhibiting or preventing the growth of fibrotic cells in the vessel wall, commonly referred to as neointima. The precise target for the radiation in the vessel is currently not known. However, it is believed that the adventitia may be a key source of growth of the neointima. Therefore, it is theorized that the entire vessel, including the adventitia should be treated with radiation.
At least one delivery device has been used for performing intravascular radiation treatment on a treatment site of the vessel. This delivery device utilizes a catheter to position a radiation source in the vessel lumen, adjacent the treatment site. The radiation source is positioned in the vessel lumen and is allowed to emit radiation until the proposed dosage is released. With this delivery device, the tissue closest to the radiation source receives a larger radiation dosage than the tissue farthest from the radiation source. Subsequently, the radiation source is removed from the vessel lumen.
However, the results obtained using this type of delivery device are not entirely satisfactory. Specifically, because the growth of the plaque inside the vessel is irregular and/or the vessel is curved, the radioactive source is not centered in the vessel relative to the vessel lamina. Thus, depending upon the dosage prescribed, this can result in undertreating certain portions of the vessel and overtreating certain other portions of the vessel. For example, certain portions of the vessel lamina will receive a larger dosage of radiation than other portions of the vessel lamina.
Undertreating with radiation can result in not inhibiting the neointima and, in some instances, can actually result in stimulating smooth muscle cell proliferation and extra-cellular matrix production. Overtreating with radiation can, for example, induce necrosis or aneurysm. Therefore, it is important to avoid overtreating and/or undertreating of a treatment site of the vessel.
One attempt to solve this problem involves accurately centering the delivery device in the vessel, relative to the vessel lumen. This can be accomplished using a variety of mechanical devices, such as a centering balloon or an expandable mechanical strut. However, these mechanical devices add excessive mass and bulk to the delivery device. This limits the usefulness of the present delivery device to relatively large vessels, i.e., 3.5 millimeters or larger and increases the risk of occluding blood flow in the vessel. Moreover, there is a risk that the delivery device will not be accurately centered.
In light of the above, it is an object of the present invention to provide a device and method for delivering a precise dose of radiation to a treatment site of a vessel without centering the delivery device. It is another object of the present invention to provide a device and method for delivering a substantially uniform dose of radiation to the vessel lamina and other areas of the vessel. Still another object of the present invention is to provide a device and method which is relatively safe and easy to use. Yet another object of the present invention is to provide a device which is relatively simple and inexpensive to manufacture.
The present invention is directed to a delivery device which satisfies these objectives. The delivery device is useful for delivering a dose of radiation from a radiation source to a treatment site of a vessel to treat a stenosis in the vessel. The delivery device includes a catheter and a delivery area which insert into the vessel. As provided herein, the delivery area includes an attenuator section which attenuates the intensity of a portion of the radiation emitting from the radiation source when a portion of the radiation source is positioned in the delivery area. In use, the attenuator section partly inhibits the intensity of radiation directed at where the vessel wall is the thinnest. This prevents overtreatment of the vessel.
As used herein, the term xe2x80x9cradiation dose profilexe2x80x9d refers to and means the cross-sectional pattern of energy being delivered from the delivery area of the delivery device. A more comprehensive definition of radiation dose profile is provided in the description section.
As used herein, the term xe2x80x9cvessel wallxe2x80x9d refers to and means the structural support of the vessel. For an artery, the vessel wall would include an endothelium, a basement membrane, a vessel intima, an eternal elastic lamina, a vessel media, a vessel external elastic lamina (hereinafter xe2x80x9cvessel laminaxe2x80x9d), and a vessel adventitia. For a diseased artery, the vessel wall can also include atherosclerotic plaque which infiltrates the vessel intima and causes stenosis of the vessel.
As provided in detail below, since the attenuator section attenuates a portion of the radiation emitting from the radioactive area, the delivery area emits a radiation dose profile which is substantially eccentric. With an eccentric radiation dose profile, more radiation can be directed at where the vessel wall is the thickest, while less radiation can be directed to where the vessel wall is the thinnest. This can be accomplished by rotating the delivery area until the attenuator section is substantially closest to the vessel lamina. Since, the attenuator section attenuates a portion of the radiation directed at where the vessel wall is the thinnest, a substantially uniform dosage of radiation is delivered to the vessel lamina at the treatment area, even though the delivery device is not centered in the vessel relative to the vessel lamina.
The attenuator section includes an attenuator material which at least partly diminishes the intensity of the radiation which emits therefrom. The attenuator material is typically a relatively dense material having a relatively high atomic number. Preferably, the attenuator material is also bio-compatible and safe for use in surgery. Materials such as gold, platinum, and tantalum can be used.
Importantly, the shape of the radiation dose profile varies according to the size, shape, and thickness of the attenuator section, as well as the attenuator material utilized. Thus, the attenuator section can be designed so that the radiation dose profile corresponds to the specific size and shape of the vessel wall. As used herein, the phrase xe2x80x9cconfiguration of the attenuator sectionxe2x80x9d shall mean the size, shape, thickness, and material utilized in the attenuator section. Also as used herein the phrase xe2x80x9cconfiguration of the vessel wallxe2x80x9d shall mean the size and shape of the vessel wall at the treatment site, including the positioning of the vessel lamina relative to the vessel lumen.
The delivery device also includes a catheter supporter which substantially inhibits rotational deformation in the catheter between a catheter distal end and a catheter proximal end. The catheter supporter allows the delivery area to be precisely rotated by the catheter proximal end to position the filter section adjacent where the vessel wall is the thinnest.
Preferably, the delivery device includes at least one marker positioned proximate the delivery area. The marker is used to indicate the location of the delivery area in the vessel. For example, the marker can be radiopaque and visible with a fluoroscope. This allows the doctor to position the delivery area adjacent the treatment area.
The invention is also a method for delivering radiation from a radiation source to a treatment site of a vessel. The method includes the steps of advancing a catheter into the vessel lumen until a delivery area is positioned substantially adjacent the treatment site, positioning at least a portion of the radiation source proximate the delivery area, and emitting a radiation dose profile from the delivery area which is substantially eccentric.
Further, the method can include the step of rotating the delivery area inside the vessel lumen until the orientation of the attenuator section is substantially closest to the vessel lamina. This step typically includes imaging the vessel to determine when a window section of the delivery area is substantially farthest away from the vessel lamina.
Preferably, the treatment site of the vessel is imaged to determine the configuration of the vessel wall proximate the treatment site. With this information, the configuration of the attenuator section can be chosen.
It is important to recognize that a device in accordance with the present invention utilizes an attenuator section proximate the delivery area so that the delivery area emits a radiation dose profile which is substantially eccentric. Therefore, the delivery device is able to deliver a substantially uniform dose to the vessel lamina, even though the delivery device is not centered relative to the vessel lamina.